The invention is directed to a cover construction for shielding containers for the transportation and/or for the storage of irradiated fuel elements, essentially consisting of an inner shielding cover and an outer transportation cover flanged on the container.
For the transportation and storage of irradiated or burned up fuel elements from nuclear reactors there are needed containers which safely hold back the radioactivity of the material. The construction of this container therefore is subject to severe requirements, above all what concerns the indestructability of the container in the case of accidents is the protection of the environment from radioactive rays.
The container for the transportation and for storage of irradiated fuel elements therefore must be constructed to be durable and sturdy and must offer a protection from radioactive rays. However, in this connection the material for radioactive shielding is so selected that the weight of the shielding, which makes up the greatest part of the weight of the transportation container, is held as small as possible for economical reasons. Besides attention must be paid that the heat of decomposition of the transported or stored fuel elements can be safely led outside.
Of especial importance with such shielding containers there is also the closing device of this shielding container, generally a cover or a cover system which after loading the container with irradiated fuel elements stays tight and which container interior must be hermetically shut off from the outer world.
With the previously known shielding containers the cover consists of, for the most part, of a cylindrical closure plug, partially applied to the container wall, which plug simultaneously carries the shielding and the sealing function. This cover is normally attached to the container with screw bolts. This container, however, has the disadvantage that a dry loading and unloading with irradiated fuel elements is only possible if an allowance is made for a contamination with subsequent expensive decontamination of the entire system. Besides frequently with such containers there is shown sealing problems, since the seal in the case of accident is laden with the total weight of the cover and the container contents. A change of seal with the loaded container is only possible by remote control whereby here also there must be taken into consideration an increased difficulty in handling through the great size of the cover.
Therefore there have already been proposed a closure apparatus for shielding containers of multipe-part cover construction. Thus it is known for example from German GM 7727690 to provide the container with an inner shielding cover and an outer security or transportation cover, the two of which are directly flanged on the container. However, here also a dry unloading is only possible if a decontamination of the entire system is undertaken. Besides there is necessary a high manipulative expense for removal of the cover, since both are constructed as flange cover and the set screws must be detached or inserted.
Therefore it was the problem of the present invention to provide a cover construction for the transportation and/or the storage of irradiated fuel elements essentially consisting of an inner shielding cover and an outer transportation cover flanged onto the container which can be handled simply and without large manipulative expense, is suited for both dry and wet loading and unloading without danger of contamination and creates no sealing problems.